Exactly like optifine meaning that it uses the same logo file that optifine would use. (assets\minecraft\textures\gui\title\mojangstudios.png) (1.16 and up) or (assets\minecraft\textures\gui\title\mojang.png) for older versions of the game (pre 1.16)

This is worth looking into if OptiFine is able to load the image before the splash screen displays, because that may mean that Splash could too.